Papermaking machine headbox slice chamber containing pivotable thin rigid plates with flexible elements attached thereto

ABSTRACT

A headbox construction for a paper making machine which includes a slice chamber having a linearly converging downstream portion and a non-linearly converging upstream portion which is connected to a preslice flow chamber. The slice chamber contains a plurality of transversely extending thin rigid plates which are curved to conform to the non-linear shape of the upstream end of the slice chamber and are pivotally supported at their upstream ends. Flexible trailing elements are attached to the downstream ends of each of the rigid plates and extend in the downstream portion of the slice chamber. These flexible trailing elements are unattached at their downstream ends. The elements and the plates each are locked in their pivotal positions or are selfpositionable so as to be solely responsive to forces exerted thereon by the stock flowing toward the slice.

United States Patent 1 Parker, deceased et al.

[ 1 June 10, 1975 1 PAPERMAKING MACHINE HEADBOX sLIcE CHAMBER CONTAININGPIVOTABLE THIN RIGID PLATES WITH FLEXIBLE ELEMENTS ATTACHED THERETO [76]Inventors: Joseph D. Parker, deceased, late of 12052 S. Gate Rd.,Roscoe, 111. 61073; by Dorothy C. Parker, executrix, 12052 S. Gate Rd.,Roscoe, 111. 61073; Richard E. Hergert, 402 Liddle St., Rockton, 111.61072; Arnold J. Roerig, 1508 S. Ridge Rd., Beloit, Wis. 53511 22 Filed:Nov. 6, 1972 21 App]. No.: 303,972

[52] US. Cl. 162/343; 162/336; 162/344 [51] Int. Cl. D2lf l/02 [58]Field of Search 162/343, 336, 347, 344

[56] References Cited UNITED STATES PATENTS 3,092,540 6/1963 Parker162/336 X Hill et al. 162/343 Parker 162/347 R [57] ABSTRACT A headboxconstruction for a paper making machine which includes a slice chamberhaving a linearly converging downstream portion and a non-linearlyconverging upstream portion which is connected to a preslice flowchamber. The slice chamber contains a plurality of transverselyextending thin rigid plates which are curved to conform to thenon-linear shape of the upstream end of the slice chamber and arepivotally supported at their upstream ends. Flexible trailing elementsare attached to the downstream ends of each of the rigid plates andextend in the downstream portion of the slice chamber. These flexibletrailing elements are unattached at their downstream ends. The elementsand the plates each are locked in their pivotal positions or areself-positionable so as to be solely responsive to forces exertedthereon by the stock flowing toward the slice.

16 Claims, 9 Drawing Figures PATENTEDJUH 10 I975 SHEET PAPERMAKINGMACHINE HEADBOX SLICE CHAMBER CONTAINING PIVOTABLE THIN RIGID PLATESWITH FLEXIBLE ELEMENTS ATTACHED THERETO BACKGROUND OF THE INVENTION Theinvention relates generally to a headbox for a paper making machine andmore particularly to a headbox construction having a tapered narrowslice chamber with a plurality of rigid plates pivotally supported attheir upstream ends so that they can float or be selfpositionable due tothe forces exerted thereon by the stock flowing toward the slice, orthey can be locked in a uniformly spaced pivotal position. The inventionprovides improvementsover structures such as US. Pat. No. 3,607,625while utilizing the principles thereof.

In headbox structures it has been proposed to advantageously employtapered slice chambers of relatively thin dimensions. These thin channelheadboxes extend in an upward direction to avoid the accumulation of airand often require turns or bends in the slice chamber. In utilizing theprinciples of US. Pat. No. 3,607,625, it has been discovered that thethin flexible trailing members cannot extend into the curved or bentportion of the slice chamber because the flexible members cannottolerate bending by the hydraulic forces without becoming distorted andunstable. These distortions will cause roughness in the discharge jetand unsatisfactory paper formation. The present invention utilizes thinrigid plates upstream of the flexible trailing members with the platesextending into the curved flow zone of the slice chamber. Problems havebeen encountered in mounting the rigid steel plates at their upstreamends due to thermal expansion and contraction and also due to thedistribution of the plates and the forces on the plates caused by thehydraulic forces of the flowing stock. In accordance with the principlesof the present invention, the plates are pivotally mounted at theirupstream ends mounted so as to be freely positionable eitherself-positionable by the flow of stock through the headbox, orpositionable by fixed spacers. The mounting preferably takes the form ofa hinged support at the upstream end of each of the plates to allow themto pivot about their point of upstream attachment. With flow through theheadbox, the sheets or plates will then be uniformly distributed in theflow channel.

It is accordingly an object of the present invention to provide animproved headbox construction using the principles of self-positionabletrailing elements of US. Pat. No. 3,607,625 and providing an improvementtherein particularly well suited for use in thin elongated tapered slicechambers.

A further object of the invention is to provide a structure of the typedescribed which solves the problems presented in a curved or angulartapered slice chamber. A general object of the invention is to provide aheadbox for a paper making machine which produces a fine scaledispersion of the fibers, which dispersion will not deteriorateexcessively as the turbulence decays.

Additional objects, advantages and features of the present invention,and alternate embodiments within the scope of the invention will becomeapparent from the teaching of the principles of the invention inconnection with the description of the preferred embodiment of thespecification, claims and drawings, in which:

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view in sectionillustrating a paper machine headbox embodying the principles of thepresent invention;

FIG. 1A is a somewhat enlarged fragmentary view showing details of FIG.1;

FIG. 2 is a somewhat schematic side elevational view of a slice chamberillustrating only one trailing element for simplicity;

FIG. 3 is an enlarged detailed segment of a portion of FIG. 2;

FIG. 4 is another enlarged detailed view of a portion of FIG. 2;

FIG. 5 is a somewhat schematic side elevational view of the preferredform of the invention showing only one trailing member for simplicity;

FIG. 6 is an enlarged detailed fragmentary view of a portion of FIG. 5;

FIG. 7 is a side elevational ing element; and

FIG. 8 is a side elevational view of another form of trailing element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, the stockis delivered in a jet stream onto a traveling fourdrinier wire 11carried over a breast roll 12.

The stock is delivered to a headbox 10 from an inlet flow pipe 13 toflow into a chamber 14 at the entry end of the headbox. The stock flowpasses through a multiplicity of diffuser nozzles 15 which are mountedon a perforate plate 15a at their upstream end and discharged through aperforate plate 15b at their downstream end. The diffuser nozzlesdischarge into a preslice chamber 16 which is provided with an air dome17. A spray 18 reduces the foaming in the air dome of the preslicechamber. The preslice chamber feeds the stock into a tapered elongateslice chamber 19 which has a somewhat enlarged tapered upper end 19a.The slice chamber is defined between a lower slice wall 24 and an upperslice wall 24a, with the upper slice wall being pivoted at 23. A jack 22mounted on the headbox raises or lowers the upper slice wall 24a. Theslice chamber 19 leads to a slice opening 20 which is controlled in sizeby vertically movable slice lip 21.

Within the long tapered chamber are a plurality of flexible trailingelements 26. These elements are supported solely at their upstream endso as to be selfpositionable by the forces of the flowing stock. Theyare supported at their upstream ends on the lower edges of rigid plates25. The outermost of these plates are curved to accommodate thecurvature of the narrowing slice chamber from its portion 19a to itsthinner portion 19, and the degree of bend in each of the plates 25diminishes from the outermost plates to the center where the centerplate is substantially flat or planar.

At their upstream ends. the plates are supported at 27.

FIG. 1A shows in greater detail the head end of the tapered slicechamber. The plates are separated by a plurality of stacked washers 25aand 25g which act as spacers. Extending through the washers and throughholes in the plates are bolts 25c and 25f. These bolts extend upwardlythrough a member 25e and extend downwardly through the bottom of theslice chamber.

view of one form of trail- The bolts are spaced in a cross-machinedirection approximately 6 inches apart. The floor of the slice chamberis threaded to receive the bolts, and nuts are threaded onto the upperends of the bolts to clamp downwardly against the plate 25e. The plate25e forms part of the assembly which supports the knuckle joint 23carrying the pivotal upper wall 24a of the slice chamber. Thus, invarious arrangements, the plates may either be fixed in their positionor be permitted to float so as to assume their natural position asdictated by the forces of the stock flowing past the plates into thetapered slice chamber.

The members 27 may be plastic rods which extend across the headbox in across-machine direction supported at their ends at the side walls of theheadbox. The rods are cylindrical in shape and arranged to permit smoothflow of stock past them without adversely affecting the flow pattern ofthe stock or providing areas where fibers or dead areas of the stock cancollect.

FIGS. 2 and indicate a form of slice chamber wherein only the lower wallis bent or curved. That is, in the upper slice chamber 19a, the walls19b and 19c are each curved so that the upper slice chamber 19a willtaper into the elongate main slice chamber 19.

In FIG. 2, the upper wall 38 of the slice chamber is flat while thelower wall 39 is curved at 39a. Thus, the upper portion 31 of the slicechamber tapers into the main narrow elongate slice chamber 30.

Similarly, in FIG. 5, the upper wall of the slice chamber 47 is flatwhile the lower wall 48 is curved at 48a so that the larger upstreamportion 45 of the slice chamber leads into the elongate thin mainportion 46 of the slice chamber.

While FIG. 5 shows only one of the plates 50 for simplicity ofillustration, it will be understood that there are a plurality of platesextending across the slice chamber each with a trailing element such as49 thereon. In this preferred arrangement, the trailing element 49, aswill be additionally described later herein, is mounted at an angle tothe plate at 54, which angle is chosen to be substantially the naturalangle between the plate 50 and trailing element 49 as the stock flowsthrough the slice chamber.

As above discussed, rigid plates are provided which are stiff enough toresist deformation by flow disturbances generated by the flow of stockaround a curve in the slice chamber. The plates are in the structures ofFIGS. 2-8, light enough to be positioned in the chamber by hydraulicforces. For this purpose, the plates are preferably of plastic which isstiff enough to resist deformation, but which has a weight thatapproaches the density of water so that the plate substantially floatsin the slice chamber and is positionable solely by the forces of thestock on the surfaces of the plate.

As previously stated, it has been discovered that the flexible trailingelements cannot extend into the curved portion of the slice chamber. Ithas also been discovered that if the flexible trailing elements arebonded to the plates at an improper angle, a disturbance in the flowwill result. Further if the bonding of the flexible trailing elements tothe plates does not conform precisely to a streamlined pattern, flowdisturbances will result in the stock flowing through the long taperedslice chamber.

As illustrated in FIG. 2, where only one trailing member is shown forthe sake of simplicity although it will beunderstood that a plurality oftrailing members such as shown in FIG. 1 will normally be employed, theplate 34 is curved to conform to the curvature of the slice chamber. Atthe upper edge of the plate 34, the plate is supported on a perforatesupport wall 35. This support wall is rigidly mounted in the headbox andprovided with a plurality of flow passages 35a, FIG. 3. Along the widthof the wall 35 extend horizontal dovetail slots 37 which receive rods orbars 36 that are welded or otherwise secured to the upper edges of theplates 34. These rods are thus pivotally mounted in the slots 37 to.permit free pivotal movement of the plates 34. This permits them to beself-positionable, and the rods 36 are usually assembled by slidingendwise into the dovetail slot 37. The support plate may be of steel orplastic, but an advantage of plastic is the diminished danger ofbuckling of the plate due to changes in temperature.

The plurality of plates 25 as shown in FIG. 1 are preferably designedtoterminate at the same location for the depth of the slice chamber 19.However, in manufacture the plates may additionally be of the same widthin a machine direction, and although different bending curvatures areplaced in the plates, the difference in position of their downstreamedge will not be that great. The flexible trailing elements, however,should be of a length so that their downstream ends will end a uniformdistance from the slice opening 20.

To accommodate a smooth flow pattern at the end of the plate, the plateis recessed at 40 as shown in FIG. 4 with the upper edge of the trailingelement 33 being bonded in the recess. Where the plate and trailingelement are formed of plastic, the two may be cemented together with anepoxy resin or may be joined by heat welding.

In the preferred form of the invention, the plates are not bent, but areflat and the flexible trailing elements are bonded to the plates at anangle, as shown in FIG. 5. In FIG. 5, the plates 50 have the trailingelements 49 within the slice chamber 46. The plates are pivotallysupported by rods 52 secured along their upstream edges and mounted indovetail grooves 53 in a perforate wall 51.

As shown in detail in FIG. 6, the trailing elements 49 are cemented tothe beveled downstream edge 54 of the plates 50 with the bevel being cutso that it is equal to the angle 48a of bend of the slice chamber. Againin this construction the plates seek their own position in accordancewith the flow of stock since they are flexibly or pivotally mounted attheir upstream edges.

Another form of construction is shown in FIG. 7 wherein a rigid plate isconnected to a flexible trailing element 64 by an extruded plasticconnector 61. By this construction, a precise and accurate curve may beobtained simply by design of the extruded connector. An additionaladvantage in this structure is that the flexible sheets may be separatedfrom the rigid plates for ease of replacement. Furthermore, by allowingthe flexible sheet to move relative to the rigid plate at a jointbetween them, it relieves the need for having precisely correct anglesof attachment of the flexible sheet to the rigid plate. The rigid platemay be formed as a single extrusion which, of course, would require adifferent extrusion for each different angle of bend for each plate.With the structure of FIGS. 7 or 8, the flat plates may be allconstructed of the same size and dimension, and the plastic extrudedconnectors may take on the different lengths and angles of curvature.FIG. 7 shows a flat plate 60 which has a hinge upstream support 66 andwhich is connected at its downstream edge to an extruded plasticconnector 61. The connector is formed with a groove 62 which provides arecess for the lower edge of the plate in order to bond the plate to theconnector.

At its lower edge the connector 61 has a groove 63 into which is bondedthe flexible trailing member 64. The connector is necked down at 65 toprovide a flexible hinge point to permit the trailing element 64 tofloat at the proper angle of curvature dependent upon the forces of theflowing stock.

In the arrangement of FIG. 8, a plate 70 is provided with a hingesupport 76 at its upstream end and is bonded at its lower edge to anextruded connector 71. The connector is provided with a dovetailed slotand a curved inner surface to receive the beaded or bulbous upper edgeof the flexible trailing element 72 in order to provide a pivotalconnection for the trailing element. This permits the trailing elementto assume its natural position as determined by the forces of theflowing stock. In each of the arrangements of FIGS. 7 and 8, differentflow circumstances will be accommodated by permitting the flexibletrailing member to assume its natural position without stress. This willalso permit manufacturing tolerances in the curvature of the slicechamber and the plate mounted therein.

The pressure differences which are generated across the plate andtrailing element support both their weights. The channels between theplates will tend to be thinner, and the pressure gradients in themhigher toward the inside of the curve. This difference between thechannels cannot be sustained in the flexible trailing elements and,therefore, is sustained by the more rigid plates.

We claim as our invention:

1. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the improvement comprising,

a plurality of rigid plates positioned in the slice chamber,

each of said plates extending transversely of said headbox andprojecting downstream generally in the direction of stock flow,

trailing elements attached to the downstream ends of said plates,

said elements being attached to said plates only at their upstream endswith their downstream portions unattached and constructed to beselfpositionable so as to be solely responsive to forces exerted thereonby the stock flowing toward the slice opening,

and means yieldably supporting said rigid plates so that the plates areself-positionable in a direction transverse of their surfaces so as tobe solely responsive to forces exerted thereon by the stock flowingtoward the slice.

2. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the construction inaccordance with claim 1 wherein said support means pivotally supportseach of the plates at their upstream ends for movement about an axisextending across the headbox parallel to the plates.

3. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the construction inaccordance with claim 1 wherein said support means includes a stationarymember in the slice chamber having a tapered slot with a downstreamopening larger than the thickness of the plate and a pivotal membersecured to the plate and being larger than said opening for pivotallysupporting each of the plates at their upstream ends for movement aboutan axis extending across the headbox parallel to the plates.

4. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the construction inaccordance with claim 1 wherein said plates have a bend in a downstreamdirection.

5. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the construction inaccordance with claim 1 wherein said slice chamber is curved to have acurved flow zone and the plates extend through said curved flow zone andare curved in the direction of curvature of the zone.

6. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the construction inaccordance with claim 1 wherein said trailing elements are attached atan angle to the plane of the downstream ends of said plates.

7. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the construction inaccordance with claim 1 wherein the downstream edge of the plates arerecessed and each trailing element for each plate is secured in saidrecess so the stock will flow smoothly past the location where thetrailing elements are attached to the plates.

8. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the construction inaccordance with claim 1 wherein the structure includes a rigid connectormember at the downstream edge of each of the plates which joins thetrailing elements to the plates.

9. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the construction inaccordance with claim 8 wherein the connector has a thin portion inadvance of the trailing element having a thickness less than thethickness of said plate.

10. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the construction inaccordance with claim 8 wherein the slice chamber is curved and theplate is flat and the connector member is curved in the direction of thecurvature of the slice chamber.

11. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the construction inaccordance with claim 8 wherein said rigid connector has a laterallyextending socket with a narrow downstream opening and the trailingelement has a bulbous upper end positioned in said socket supporting thetrailing element.

12. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the improvement comprising,

a rigid plate positioned in the slice chamber,

said plate extending transversely of said headbox and projectingdownstream generally in the direction of stock flow,

a trailingelement attached to the downstream end of said plate, saidelement being attached to said plate only at its upstream end with itsdownstream portion unattached and constructed to be self-positionable soas to be solely responsive to forces exerted thereon by the stockflowing toward the slice, and means supporting said rigid plate so thatthe plate is yieldable in a direction transverse of its surfaces and isself-positionable so as to be solely responsive to forces exertedthereon by the stock flowing toward the slice opening.

13. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the improvement comprising,

a rigid member positioned in the slice chamber,

said member projecting downstream generally in the direction of stockflow,

means supporting said member only at its upstream end and accommodatingpivotal movement of said member so that the member is self-positionableresponsive solely to forces exerted thereon by the stock flowing towardthe slice opening,

and a flexible element being attached to said member only at itsupstream ends with its downstream portion unattached and constructed tobe selfpositionable so as to be solely responsive to forces exertedthereon by the stock flowing toward the slice opening.

14. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the improvement comprising:

a rigid plate positioned in the slice chamber,

said plate extending transversely of said headbox and projectingdownstream generally in the direction of stock flow,

a trailing element attached to the downstream end of said plate,

said element being attached to said plate only at its upstream end withits downstream portion unattached and constructed to beself-positionable so as to be solely responsive to forces exertedthereon by the stock flowing toward the slice,

and means connecting said trailing element to said plate permitting freeand independent positioning at the point of attachment,

said connecting means including a bulbous portion on the upstream edgeof the trailing element mounted for free pivotal movement in a slot atthe downstream edge of the plate.

15. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the improvement comprising:

a rigid plate positioned in the slice chamber,

said plate extending transversely of said headbox and projectingdownstream generally in the direction of stock flow, a trailing elementattached to the downstream end of said plate, said element beingattached to said plate only at its upstream end with its downstreamportion unattached and constructed to be self-positionable so as to besolely responsive to forces exerted thereon by the stock flowing towardthe slice, and means connecting said trailing element to said platepermitting free and independent positioning at the point of attachment,said connecting means including a separate plastic connector having aflexible hinge portion permitting free bending of the connecting means.16. In a headbox for delivering stock to a forming surface, the headboxhaving a chamber leading to a slice chamber with a slice opening, theimprovement comprising:

top and bottom slice walls defining a slice chamber therebetween withthe slice chamber shaped to extend nonlinearly from the headbox chamberto the slice opening;

a plurality of trailing members positioned within the chamber, saidtrailing members having a first rigid plate portion shaped to generallyconform to the nonlinear shape of the slice chamber and having a secondflexible downstream trailing element portion with their downstream endsfree of support; and support means in the slice chamber supporting saidmembers at their upstream ends including a pivotal mount for the rigidplate portion of the trailing members supporting them pivotally at theirupstream ends.

1. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the improvement comprising,a plurality of rigid plates positioned in the slice chamber, each ofsaid plates extending transversely of said headbox and projectingdownstream generally in the direction of stock flow, trailing elementsattached to the downstream ends of said plates, said elements beingattached to said plates only at their upstream ends with theirdownstream portions unattached and constructed to be self-positionableso as to be solely responsive to forces exerted thereon by the stockflowing toward the slice opening, and means yieldably supporting saidrigid plates so that the plates are self-positionable in a directiontransverse of their surfaces so as to be solely responsive to forcesexerted thereon by the stock flowing toward the slice.
 2. In a headboxfor delivering stock to a forming surface, the headbox having a slicechamber and a slice opening, the construction in accordance with claim 1wherein said support means pivotally supports each of the plates attheir upstream ends for movement about an axis extending across theheadbox parallel to the plates.
 3. In a headbox for delivering stock toa forming surface, the headbox having a slice chamber and a sliceopening, the construction in accordance with claim 1 wherein saidsupport means includes a stationary member in the slice chamber having atapered slot with a downstream opening larger than the thickness of theplate and a pivotal member secured to the plate and being larger thansaid opening for pivotally supporting each of the plates at theirupstream ends for movement about an axis extending across the headboxparallel to the plates.
 4. In a headbox for delivering stock to aforming surface, the headbox having a slice chamber and a slice opening,the construction in accordance with claim 1 wherein said plates have abend in a downstream direction.
 5. In a headbox for delivering stock toa forming surface, the headbox having a slice chamber and a sliceopening, the construction in accordance with claim 1 wherein said slicechamber is curved to have a curved flow zone and the plates extendthrough said curved flow zone and are curved in the direction ofcurvature of the zone.
 6. In a headbox for delivering stock to a formingsurface, the headbox having a slice chamber and a slice opening, theconstruction in accordance with claim 1 wherein said trailing elementsare attached at an angle to the plane of the downstream ends of saidplates.
 7. In a headbox for delivering stock to a forming surface, theheadbox having a slice chamber and a slice opening, the construction inaccordance with claim 1 wherein the downstream edge of the plates arerecessed and each trailing element for each plate is secured in saidrecess so the stock will flow smoothly past the location where thetrailing elements are attached to the plates.
 8. In a headbox fordelivering stock to a forming surface, the headbox having a slicechamber and a slice opening, the construction in aCcordance with claim 1wherein the structure includes a rigid connector member at thedownstream edge of each of the plates which joins the trailing elementsto the plates.
 9. In a headbox for delivering stock to a formingsurface, the headbox having a slice chamber and a slice opening, theconstruction in accordance with claim 8 wherein the connector has a thinportion in advance of the trailing element having a thickness less thanthe thickness of said plate.
 10. In a headbox for delivering stock to aforming surface, the headbox having a slice chamber and a slice opening,the construction in accordance with claim 8 wherein the slice chamber iscurved and the plate is flat and the connector member is curved in thedirection of the curvature of the slice chamber.
 11. In a headbox fordelivering stock to a forming surface, the headbox having a slicechamber and a slice opening, the construction in accordance with claim 8wherein said rigid connector has a laterally extending socket with anarrow downstream opening and the trailing element has a bulbous upperend positioned in said socket supporting the trailing element.
 12. In aheadbox for delivering stock to a forming surface, the headbox having aslice chamber and a slice opening, the improvement comprising, a rigidplate positioned in the slice chamber, said plate extending transverselyof said headbox and projecting downstream generally in the direction ofstock flow, a trailing element attached to the downstream end of saidplate, said element being attached to said plate only at its upstreamend with its downstream portion unattached and constructed to beself-positionable so as to be solely responsive to forces exertedthereon by the stock flowing toward the slice, and means supporting saidrigid plate so that the plate is yieldable in a direction transverse ofits surfaces and is self-positionable so as to be solely responsive toforces exerted thereon by the stock flowing toward the slice opening.13. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the improvement comprising,a rigid member positioned in the slice chamber, said member projectingdownstream generally in the direction of stock flow, means supportingsaid member only at its upstream end and accommodating pivotal movementof said member so that the member is self-positionable responsive solelyto forces exerted thereon by the stock flowing toward the slice opening,and a flexible element being attached to said member only at itsupstream ends with its downstream portion unattached and constructed tobe self-positionable so as to be solely responsive to forces exertedthereon by the stock flowing toward the slice opening.
 14. In a headboxfor delivering stock to a forming surface, the headbox having a slicechamber and a slice opening, the improvement comprising: a rigid platepositioned in the slice chamber, said plate extending transversely ofsaid headbox and projecting downstream generally in the direction ofstock flow, a trailing element attached to the downstream end of saidplate, said element being attached to said plate only at its upstreamend with its downstream portion unattached and constructed to beself-positionable so as to be solely responsive to forces exertedthereon by the stock flowing toward the slice, and means connecting saidtrailing element to said plate permitting free and independentpositioning at the point of attachment, said connecting means includinga bulbous portion on the upstream edge of the trailing element mountedfor free pivotal movement in a slot at the downstream edge of the plate.15. In a headbox for delivering stock to a forming surface, the headboxhaving a slice chamber and a slice opening, the improvement comprising:a rigid plate positioned in the slice chamber, said plate extendingtransversely of said headbox and pRojecting downstream generally in thedirection of stock flow, a trailing element attached to the downstreamend of said plate, said element being attached to said plate only at itsupstream end with its downstream portion unattached and constructed tobe self-positionable so as to be solely responsive to forces exertedthereon by the stock flowing toward the slice, and means connecting saidtrailing element to said plate permitting free and independentpositioning at the point of attachment, said connecting means includinga separate plastic connector having a flexible hinge portion permittingfree bending of the connecting means.
 16. In a headbox for deliveringstock to a forming surface, the headbox having a chamber leading to aslice chamber with a slice opening, the improvement comprising: top andbottom slice walls defining a slice chamber therebetween with the slicechamber shaped to extend nonlinearly from the headbox chamber to theslice opening; a plurality of trailing members positioned within thechamber, said trailing members having a first rigid plate portion shapedto generally conform to the nonlinear shape of the slice chamber andhaving a second flexible downstream trailing element portion with theirdownstream ends free of support; and support means in the slice chambersupporting said members at their upstream ends including a pivotal mountfor the rigid plate portion of the trailing members supporting thempivotally at their upstream ends.